The present invention is related to the field of manually operable presses. More specifically, the invention is related to manually operable presses comprising a manually pivotable actuating lever for effecting a forward press stroke and a return stroke of a press slide or ram, a mechanical return stroke interlock inhibiting a return movement of the press before the press slide has come to a lower end position. Still more specifically, the invention is related to such a press also having a cam plate within the return stroke interlock connected for being pivoted together with the actuating lever, the cam plate having a groove-shaped guide cam provided with a plurality of lock protrusions, a spring-biased lock pin running along the guide cam and being adapted to run freely along the guide ram in an operational direction but being inhibited by the lock protrusions within the guide cam from running in a direction opposite the operational direction.
A manually operable press of the kind specified at the outset is disclosed in European patent specification 0 622 175 B1.
Manually operable presses of this kind are mainly used in piecework production lines where the workers are paid according to the number of the processed workpieces. Manually operable presses require to exert a force which increases towards the end of the press stroke. Workers using manually operable presses, therefore, tend to execute the work or press stroke only incompletely and to initiate the relaxation or reverse stroke already prior to having reached the intended lower dead position or end position of the press slide. As a consequence, when the press operation has not been exactly completed, the workpieces must be thrown away or at least have a minor quality.
In order to avoid such consequences, the prior art press according to the European patent specification mentioned above, has a mechanical return stroke lock comprising a cam plate with a groove-shaped control cam and a spring-biased lock pin engaging same. The control cam consists of several sections, two of them extending in a peripheral direction, whereas the third section essentially extends radially and inwardly and a fourth section extending radially outwardly and, along the periphery, back to the first section. Between the first and the second section, there is a lock protrusion which can be surmounted by the lock pin only in a direction from the first towards the second section.
The lock pin itself is spring-biased in an axial direction and is journalled within a sliding block which, in turn, is configured to be moved in a radial direction under the action of a spring.
In the course of the work stroke of the press, the lock pin first runs on the groove bottom from the first to the second section. As soon as the second section has been reached, the worker cannot move the actuating lever again back and upwardly because the lock pin will then come to rest against the lock protrusion which inhibits a further movement of the cam plate being connected for a rotation together with the actuating lever. Only during a further movement of the cam plate along the operational direction and, hence, a movement of the actuating lever downwardly, the rest pin comes into the third cam section and is there moved radially and outwardly together with the sliding block. Only now a return stroke is possible during which the lock pin runs along the fourth cam section in a peripheral direction and radially outwardly, until it again reaches the first cam section.
By doing so, it is guaranteed that the press stroke is first executed completely before the return stroke may be initiated.
However, due to faulty alignment of the workpieces to be pressed together and/or due to wrong workpiece tolerances, it may happen once in a while that the press stroke cannot be executed completely because the lower end position of the press stroke cannot be reached due to the dimensions and/or the orientations of the workpieces with respect to one another. In order to enable discharging of such faulty workpieces, the control cam of the prior art press comprises an arcuate slot being accessible from the outside making the second and the third section of the control cam accessible. If the press is jammed as described before, the lock pin may be pushed back in an axial direction from outside by introducing a thin device through the slot, thus making it possible to rotate the control cam back from that position and letting the lock pin run along the control cam in a direction opposite the operational direction.
Although this prior art press provides an efficient return stroke lock also enabling to unlock same in an emergency situation, this prior art return stroke lock nevertheless comprises a number of disadvantages in connection with the unlocking in an emergency situation.
First, it is disadvantageous to provide a relatively large slot in the groove bottom of the control cam because dirt may penetrate into the return stroke lock, in particular into the control cam. Therefore, it may happen that the control cam will be repleted with dirt, chips etc. over longer periods of time so that at the end the lock pin will be able to surmount the lock protrusion also in a direction opposite the operational direction.
A second disadvantage consists in the fact that unlocking the lock pin by means of a thin device is relatively complicated. For example It happens all the time that the device will slip off the lock pin before the latter has surmounted the lock protrusion so that the unlocking operation must be repeated several times before it is successful. This is of particular disadvantage when the device and/or the lock pin are covered with oil or another lubricant. Such time-consuming unlocking operations, further, do not make sense, in particular in connection with piecework production lines.
Still another significant disadvantage of the prior art unlocking system becomes apparent in a situation where a worker has come between the press ram and the workpiece to be processed with his finger, his hand or a piece of skin and the skin is then jammed and injured during the execution of the press stroke which may result in severe injuries. In particular in such an emergency situation, the unlocking system in the prior art press is very disadvantageous because one has found that the worker in most cases does not have enough patience to carefully locate the lock pin within the slot by means of the thin device in order to unlock same. In most cases the worker will be so nervous and impatient that he will tear his hand out of the press, thus making the injuries still worse.
Bearing the above in mind, it is an object underlying the present invention to improve a press of the kind specified at the outset such that the return stroke lock on the one hand has a very simple design and, on the other hand, may be unlocked quite easily.
According to the present invention, this object is achieved by a manually operable press comprising a manually pivotable actuating lever for effecting a forward press stroke and a return stroke of a press slide or ram, a mechanical return stroke lock inhibiting a return movement of the press before the press slide has come to a lower end position of the press stroke, a cam plate within the return stroke interlock, connected for being pivoted together with the actuating lever, the cam plate having a groove-shaped guide cam provided with a plurality of lock protrusions, a spring-biased lock pin running along the guide cam and being adapted to run freely along the guide ram in an operational direction but being inhibited by the lock protrusions within the guide cam from running in a direction opposite the operational direction, an opening each provided in the guide cam at the lock protrusions, unlocking pins provided in each of the openings, the pins being adapted to be actuated from outside the press for bringing the lock pin out of engagement with the lock protrusions, thus allowing the lock pin to run in the opposite direction when the unlocking pins are actuated.
First of all, the invention has the advantage that an unlocking pin projects outwardly from the cam plate, whereby the unlocking pin is accessible at any time and needs not to be introduced first. By providing the unlocking pin in the area of the lock protrusion, it will exactly come into contact with the lock pin when the latter comes to rest on the lock protrusion.
The inventors of the present application have found that a slot-shaped opening within the groove bottom of the control cam is not mandatory. Instead, it is sufficient to provide a bore in the area of the lock protrusion receiving the unlocking pin, because if one of the malfunction or emergency situations occur, as have been described above, the lock pin is resting against the lock protrusion anyway because the operator of the press instinctively moves the actuating lever backwards, i.e. upwardly. This becomes apparent by an impingement during the movement of the actuating lever, upon which the operator only needs to press the unlocking pin inwardly so that the lock pin is contacted in any case and it must not be expected that the unlocking pin will slide away from the lock pin.
If the opening is just a circular opening tightly receiving the unlocking pin, a further advantage of this design is that no dirt can penetrate into the guide cam because the latter is no more accessible from the outside when the opening is entirely closed by the unlocking pin received therein.
In this connection it is particularly preferred when the unlocking pin is spring-biased.
This measure has the advantage that the unlocking pin will automatically return into its initial position when it is released by the operator, after the lock pin has surmounted the lock protrusion in a direction opposite the operational direction.
Moreover, it is preferred when the unlocking pin extends parallel to the lock pin.
This has the advantage that the lowermost force is required to push the lock pin axially out of the control cam.
Still more specifically, it is preferred when the unlocking pin is interconnected with an emergency actuator button which, preferably, is arranged axially displaceable on the cam plate and, still more preferably, is captivated on a guide sleeve being attached to the cam plate from outside which, particularly, is provided with a collar associated to a shoulder on the emergency actuator button.
These measures have the advantage that although only a relatively thin unlocking pin may project into the control cam, the unlocking pin, from the exterior, however, is connected with a relatively large emergency actuator button being large enough so that the operator in a malfunction situation or an emergency situation may simply push thereon uncontrolled. Considering that most conventional manually operable presses are provided with a return spring pulling the press slide upwardly, particular advantages become apparent in situations where body members are jammed within the press. The operator, being shocked by such a situation, will immediately let the actuating lever go, whereupon the press ram will move upwardly a little bit until the lock pin impinges on the next lock protrusion. The operator may then press the emergency actuator button with his free hand, whereupon the entire return movement of the press ram in an upward direction is effected under the action of the return spring, i.e. automatically.
There is a particular advantage with the emergency actuator button if the control cam has a plurality of lock protrusions because then all of the corresponding unlocking pins may be actuated by one and the same emergency actuator button effecting that all of the unlocking pins are simultaneously inserted into the control cam.
Arranging the emergency actuator button on a guide sleeve having a collar has a plurality of design advantages. In particular when the emergency actuator button has a central opening through which fastener elements become accessible, which fastener elements are provided for attaching the guide sleeve to the cam plate, a particularly simple assembly of the manual emergency unlocking system becomes possible also in connection with already existing presses even if those are provided with the slot in the groove bottom of the control cam mentioned above.
This is because the unlocking pins may be mounted on the emergency actuator button in a correct position relative to one another, whereupon the guide sleeve may be inserted through the emergency actuator button and then be attached to the cam plate. By providing mounting bores, e.g. for corresponding bolts, it is guaranteed that the unlocking pins extend into the slot exactly in the area of the lock protrusions.
The central opening is then covered by means of a cover plate so that also in the case of such add-on solutions for existing presses, one has the advantage that any penetration of dirt into the area of the control cam is avoided because the emergency actuator button entirely covers still open areas of the slot.
Generally speaking it is still preferred when there is a compression spring provided between the emergency actuator button and the cam plate, the compression spring pushing the emergency actuator button against the collar of the guide sleeve.
This measure, too, has advantages with regard to the particular design because it is no more necessary to provide each and every unlocking pin with its own return spring. Instead, the return action is effected by the compression spring moving the emergency actuator button away from the cam plate.
Further advantages will become apparent from the description and the enclosed drawing.
It goes without saying that the features mentioned before and those that will be explained hereinafter, may not only be used in the particularly given combination, but also in other combinations or alone without leaving the scope of the present invention.